Evidence is unbidden because it does not affirm the priors

A nice summary from Does Inequality Reduce Economic Growth: A Skeptical View by Timothy Taylor.

hose who find the rise in income inequality over the last few decades to be concerning, like me, can find themselves facing the "so what?" question. Is my concern over rising inequality an ethical or perhaps an aesthetic judgement, and thus a personal preference where economics really doesn't have much guidance to offer? Faced with this possibility, the temptation arises to claim the following syllogism: 1) We have experienced greater inequality, which is undesirable. 2) We have experiences slower economic growth, which is undesirable. 3) Therefore, greater inequality causes slower economic growth.

A variety of studies have undertaken to prove a connection from inequality to slower growth, but a full reading of the available evidence is that the evidence on this connection is inconclusive. For example, the OECD has recently published a report called "In It Together: Why Less Inequality Benefits All," and Chapter 3, titled "The Effect of Income Inequality on Economic Growth," offers an OECD analysis seeking to connect the two. But before presenting the new study, the OECD report has the honesty and forthrightness to point out that the full body of literature on this subject is inconclusive as whether such a relationship even exists--and if so, in what direction the relationship goes.

[snip]

Given the competing theoretical explanations, what does the actual evidence say? The OECD writes
(pp. 61-62):

The large empirical literature attempting to summarize the direction in which inequality affects growth is summarised in the literature review in Cingano (2014, Annex II). That survey highlights that there is no consensus on the sign and strength of the relationship; furthermore, few works seek to identify which of the possible theoretical effects is at work. This is partly tradeable to the multiple empirical challenges facing this literature.

The passionate discussions about inequality over the past few years have struck me as primarily useful political cudgels to beat a political agenda of totalitarianism and coercion fueled by emotionalism.

We know that very extreme inequality has a negative consequence but that is at levels of inequality that are not seen outside of totalitarian dictatorships. The case that inequality in the ranges seen within OECD countries has always rested on logical extensions of unproven assumptions and very little empirical evidence. And as Taylor and the OECD report both aver, that is still the case.

Like climate, like economic development, like education, etc. the systems are far more complex than our current comprehension and the case for action is inadequate. That fact is frustrating to those compelled to action by faith-based beliefs but still does not overcome the fact that we simply do not know enough to intelligently make evidence-based decisions that can confidently yield beneficial outcomes and avoid unintended negative outcomes.

Scratch someone concerned about inequality and you likely have some mix of good intentions, poor epistemological awareness, and a reflexive totalitarian who wishes to force others to undertake the actions called for by their own faith. Evidence is unbidden because it does not affirm the priors.